REVIEWS 281 



There are certain lead and copper veins of doubtful affiliation which 

 do not appear to belong to any of the groups described and which seem 

 to have no genetic relation to igneous rocks. They are, so far as devel- 

 oped, of small importance. 



The copper deposits in sandstone, which, in part at least, replace 

 carbonaceous material and which appear to have no direct connection 

 with igneous rocks, form a relatively unimportant, but an exceedingly 

 interesting group. These ores are mainly in the "Red Beds." The 

 minerals are chalcocite, bornite, chalcopyrite, pyrite, malachite, azurite, 

 silica, barite, and gypsum. Frequently these deposits replace coal. 

 Some ores carry a few ounces of silver to the ton of chalcocite. 



It is believed that the metals known to have been present in pre- 

 Cambrian areas were leached out of these as sulphates, and rede- 

 posited in sediments that collected in inland lakes or seas. In part 

 they were deposited as the solid detrital sulphides. When surface 

 waters leached such beds, copper was dissolved. The waters of the 

 Red Beds are known to be rich in chlorides and sulphates. From the 

 organic matter in the beds, hydrogen sulphide would be added, and 

 this would readily precipitate copper sulphide. 



Pages 82 to 348 contain detailed descriptions of the many mining 

 districts. W. H. E. 



Syllabus of a Course of Lectures on Economic Geology. By John 

 C. Branner. Published by Stanford University. 3d ed., 

 ion. Pp. 503. 

 This syllabus is intended for the use of students in college and after- 

 ward. The method of treatment of the various subjects is mainly 

 by outlines, which are to be expanded by notes from lectures, readings, 

 and observation, and written out on blank pages opposite the outlines. 

 Numerous text figures and cross-sections of mines add greatly to the 

 value of the book. The references are full, well chosen, and up to date. 



W. H. E. 



Descriptive Mineralogy, with Especial Reference to the Occurrences 

 and Uses of Minerals. By Edward Henry Kratjs. Ann 

 Arbor, Mich.: George Wahr, 1910. 

 The book contains 334 pages of text and about the same number of 

 blank pages for students' notes. It is designed primarily for the stu- 

 dent of general mineralogy, with little reference to microscopical optics. 



